Spermatogenesis and sperm maturation result in dramatic changes in the plasma membrane of the developing male gamete. These changes include the acquisition of cell surface molecules required for fertilization. In the mouse, one of these cell surface molecules is the enzyme UDP-galactosyltransferase (GT). GT is a unique molecule in the reproductive tract as it may exist in three different forms: as a plasma membrane component, as a constituent of the golgi membrane and as a secretory product of the somatic cells in the seminiferous and epididymal epithelia. It has not been established whether a biochemically distinct form of GT resides in each compartment. Neither has it been established how the biosynthesis of these molecules is regulated. However, as the structure and function of the male reproductive tract are hormonally regulated, both the synthesis and the distribution of GT among the three compartments may be influenced by hormones. Recently, we have developed two reagents with which to carefully examine the source, biochemistry and regulation of germ cell surface GT. These reagents are (1) a polyclonal, monospecific antiserum against bovine GT which specifically binds GT on the mouse sperm plasma membrane, and (2) a cloned cDNA for murine GT mRNA. Using these specific reagents, we propose the following experiments: First, we will establish which germ cells have a cell surface GT and whether they synthesize the protein and insert it into their plasma membranes. We will also explore the alternative possibility that germ cell surface GT is an extrinsic membrane component which is derived from secretions of the Sertoli cell and the epididymal epithelium. Second, we will compare the biochemical structures of galactosyltransferase recovered from the plasma membrane, from the golgi membrane, and from the pool of proteins secreted by Sertoli cells and the epididymal epithelium. Additionally, we will determine whether each form of GT is encoded by a distinct GT mRNA. Third, we will compare the hormonal regulation of germ cell surface GT, golgi membrane GT and secreted GT. Completion of these experiments will result in the first thorough analysis of the distribution, source, biochemistry and regulation of a germ cell membrane protein required for fertilization.